Preview features [1] are fully supported — and are part of the official Java SE specification — they're just not finalised or "permanent" (and are, therefore, d

Preview features [1] are fully supported — and are part of the official Java SE specification — they're just not finalised or "permanent" (and are, therefore, disabled by default). I.e. the API might experience some changes due to feedback, so those who wish to use it acknowledge, by means of the --enable-preview flag, that they accept the possibility of the API changing. However, an API is marked as Preview (as opposed to incubator[2]) only when it is close to being finalised, meaning that we believe it can be finalised in two releases (one year). [1]: https://openjdk.java.net/jeps/12 https://openjdk.java.net/jeps/12 [2]: https://openjdk.java.net/jeps/11 https://openjdk.java.net/jeps/11